Question

A constant force acting on a body of mass of $5 \,kg$ change its speed from $5\, m s^{-1}$ to $10\, ms^{-1}$ in $10\, s$ without changing the direction of motion. The force acting on the body is

• A. $1.5 \,N$
• B. $2 \,N$
• C. $2.5 \,N$
• D. $5\, N$

Answer 1

Answer: (C)

$2.5 \,N$

Answer 2

Here, $m=5 Kg$, $u=5\, m s^{-1}$, $v=10 \,m s^{-1}$, $t=10\, s$ Using $v=u+a t$ $a=\frac{v-u}{t}$ $=\frac{\left(10-5\right)m s^{-1}}{10 \, s}$ $=0.5 \,m s^{-2}$ As $F=ma$ $\therefore\,$ $F=\left(5\, kg\right)$ $\left(0.5\,m s^{-2}\right)$ $=2.5 \,N$